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A circuit model for characterizing the electrical characteristics of solid-state electronic devices. Commonly used solid-state electronic devices include crystal diodes, crystal triodes and field effect transistors. They are combined with other electronic components to form various circuits with different functions.
In order to analyze these circuits, solid-state electronic devices must be represented as simple circuit models composed of some circuit elements. These circuit elements can be passive electronic elements, controlled current sources or controlled voltage sources (see circuit).
Although this equivalent circuit can only approximately reflect the external electrical characteristics of such electronic devices, it plays a very important role in the analysis and design of electronic circuits. With the rapid development of integrated circuits and computer-aided analysis and design methods, it is more and more important to establish a more reasonable circuit model of solid-state electronic devices.
Generally speaking, according to the magnitude of signal amplitude, the equivalent circuits of solid-state electronic devices can be divided into two categories: small signal equivalent circuits and large signal equivalent circuits. Crystal diode AC small signal equivalent circuit, its main equivalent circuit elements are parallel AC resistance R and capacitor C (figure 1). R is defined as the ratio of the slight change of diode terminal voltage to the slight change of current.
The value of r varies with the DC operating point of the diode. Capacitor c consists of barrier capacitor CT and diffusion capacitor CD in parallel. H parameter and y parameter of transistor AC small signal equivalent circuit. Transistors operating under small AC signals can be represented by an active two-port network composed of linear elements (see network topology).
Baidu Encyclopedia-Equivalent Circuit of Solid State Electronic Devices